In certain localities where water contains a high mineral content, sediment or lime can build up in a water heater tank. With a gas fired water heater, the gas burner is located generally in a compartment beneath the lower head, and the buildup of sediment on the lower head acts as an insulating layer to reduce the rate of heat transfer from the burner to the water in the tank. As the insulating layer increases in thickness, overheating of the lower head can result, which can, in some instances, result in rupture of the head.
To aid in preventing the buildup of sediment on the lower head of a gas fired water heater, agitator systems have been incorporated to agitate the water in the lower end of the tank. In a conventional water heater, as a faucet is opened in the water piping system, heated water will be drawn from the water heater and cold water will be introduced into the lower portion of the water heater tank. In the agitation systems as used in the past, the entry of the cold water has been employed to create the agitating action to prevent buildup of sediment, as dislosed in U.S. Pat. Nos. 4,257,355 and 4,157,077.
The commercially available agitation systems are intended to disperse existing scale on the lower head of the tank, and it is apparent that a better approach would be to prevent or minimize the formation of scale. One manner of minimizing the formation of scale would be to reduce the temperature of the heat transfer surface, i.e. the lower head of the tank.
Furthermore, the existing agitating systems perform the agitation function only during periods of water demand. Therefore, there is no agitation of the scale during periods when water is not being drawn from the tank, and it would clearly be a better practice to provide water circulation and cooling of the lower head during all burner operating periods.